If your guns are both semi auto, the M41K should be fine, and I say that, but AAC people claim the M41K will take more abuse than anything else on the market... which is a bold claim when the M4QD and Surefire cans are all inconel.
The 2kmod7 is a better product, so if you have the money to burn, buy it.
My personal opinion is assinine in most people's reasoning, but I would go with a 7.62 SD, because it is only 22ounces, and it will suppress both the .762 and .223, using a M41K mount. (comparable to KAC's M4 QD in terms of weight.)
The SCARMOR finish comes on the 7.62 SD as far as I know, and the unit is a little cheaper than a mod7.
I have pretty good hearing, so I'm guessing the 7.62SD would sound better on an M4 anyway. (more volume, larger bore diameter ='s less back pressure hopefully, and maybe less risk of an errant, shit round causing a baffle strike.)
That is 8" long though, so it makes your 11.5 a 19.5" working length.
I don't mind that. I just want to ditch ear plugs and save money.